Investigation of CO and CO₂ Adsorption on Tetragonal and Monoclinic Zirconia

Abstract

The adsorption of CO and CO2 on tetragonal and monoclinic ZrO2 was investigated using infrared spectroscopy and temperature-programmed desorption spectroscopy. For this study, samples were prepared of tetragonal ZrO2 (t-ZrO2) with surface areas of 20 and 187 m2/g and of monoclinic ZrO2 (m-ZrO2) with surface areas of 19 and 110 m2/g. The CO2 adsorption capacity of m-ZrO2 is more than an order of magnitude higher than that of t-ZrO2. The principal species observed on m-ZrO2 are HCO3 - and m- and b-CO3 2-, whereas the principal species observed on t-ZrO2 are p- and b-CO3 -. The higher CO2 adsorption capacity of m-ZrO2 is attributed to the higher concentration and basicity of the hydroxyl groups on this polymorph, as well as the stronger Lewis acidity of Zr4+ cations and the stronger Lewis basicity of O2- anions. Depending on the adsorption temperature, the CO adsorption capacity of m-ZrO2 is 5- to 10-fold higher than that of t-ZrO2. Below 450 K, CO is adsorbed as HCO3 - and CO3 2- species on both polymorphs of ZrO2. At higher temperatures, only CO3 2- and HCOO species are observed. The CO adsorption capacity of m-ZrO2 is higher than that of t-ZrO2 because of the greater strength of the adsorption centers on this phase.

Hydrogen Utilization in Green Fuel Synthesis via CO2 Conversion to Methanol over New Cu-Based Catalysts

“…The first one should be the oxide phase, with basic properties, which attends to adsorb and activate CO2 molecules for running hydrogenation to methanol, through the formation of a formate as intermediate [46]. In more detail, the CO2 chemisorption can occur both via Zirconia Lewis basic sites [47,49,50], as well as by action of metal alkaline ZnO phase which enhances the affinity of Cu (+) -O to CO2 [18]. As proof, in our previous works we have attested a larger CO2 uptake, consequently to a greater concentration of basic sites [33,34].…”

“…Therefore, the catalyst performance depends on the right "deal" between the two catalytic functionalities [3,38,45,46,[49][50][51].…”

Review: monoclinic zirconia, its surface sites and their interaction with carbon monoxide

“…Most of the studies on the interaction with CO have been carried out using infrared spectroscopy 5,18,19,[22][23][24] . However, studies using other techniques, such as temperature-programmed methods 20,21,28,30 , calorimetry 27,31,32 , and gravimetry 33,34 , as well as theoretical studies 22,28 have been published.…”

“…This choice is made for simplicity and clarity, as monoclinic and tetragonal zirconias differ in, e.g., surface hydroxyl species 7,25 and acidity/basicity 7,24,30 , further demonstrated in their interactions with CO 7,25,30 and in their catalytic activity, e.g., in water-gas shift 11,12 . More information can also be found in the reviews by Dyrek et al 35 and Hadjiivanov 36 .Most of the pre-1993 works included in this paper were reviewed 20 years ago by Nawrocki et al 37 in the context of chromatography; this review is providing an update with work reported since 1993, from the perspective of catalysis.…”

The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated by the Behavior of Sulfated Zirconia Catalysts

“…Consistent with this hypothesis, Pokrovski et al [60] found that, at the same temperature, much more CO or CO 2 per surface unit area can be chemisorbed on monoclinic than on tetragonal zirconia. More important for the discussion here, Li et al [54] detected a significantly higher uptake of SO 3 by monoclinic than by tetragonal zirconia at a temperature of 473 K. One may speculate that adsorbed SO 3 or sulfate will also reduce the difference in surface energies between the two phases and will, similar to water, diminish the particle size for the stability crossover.…”